Wen Lei

A critical challenge in developing multifunctional ceramic components is the integration of different functional units, which necessitates solving the problem of co-firing incompatibility between dissimilar ceramics. Here, warpage-free and crack-free Ba₃Ti₄Nb₄O₂₁ (BTN) ceramic/Ni_0.6Zn_0.4Fe_1.98O₄ (NZF) ferrite laminates with strong interfacial bonding were successfully co-fired using the solid-state reaction method. The co-firing compatibility was achieved by investigating the sintering shrinkage behavior of NZF ferrites with different particle sizes while preserving the magnetic properties of NZF. The internal stress distribution within the heterostructure was analyzed via finite element simulation, which indicated that BTN and L-NZF (with a relatively large particle size) possess excellent co-firing matchability. Moreover, the phase composition, elemental distribution, and microstructure of the BTN/L-NZF interface were systematically investigated, and the reaction zone induced by direct co-firing was identified. The results demonstrate a tightly bonded interface with minimal elemental interdiffusion. A thin (18.6 nm) M-type barium ferrite (BaM) interphase layer formed at the interface due to the reaction between BTN and L-NZF, which significantly strengthened the interfacial adhesion through the introduction of semicoherent interface at the initially incoherent boundary. Ion interdiffusion was suppressed by the BaM layer. Among the ions, Fe³⁺ diffused the farthest but with a limited distance of only 63 nm, which did not noticeably affect the dielectric properties of BTN. This work demonstrates the potential of BTN/NZF for multilayer devices such as filters and offers an approach to tailoring interfacial properties in co-fired ceramics.

In this communication, a wideband and wide axial ratio bandwidth (ARBW) metantenna based on magneto-electric (ME) dipole is proposed for Ka-band satellite communications (SATCOMs). The ME dipole source incorporates slotting in the planar radiator to achieve miniaturization and is integrated with a linear-to-circular polarization converter (LTCPC) operating within the matched band to enable circularly polarized (CP) radiation. To evaluate its performance, a 4×4 fixed-beam array was designed, fabricated, and tested. Simulation results show an ARBW below 3 dB spanning 26.85-40.5 GHz (40.5%) and an impedance bandwidth covering 26.55-40.1 GHz (40.7%). Measured results agree well with simulations. The radiation characteristics demonstrate high polarization isolation, and the co-polarization type can be switched by rotating the LTCPC. Upon integration with a power divider to form a broadside array, the antenna achieves stable gain up to 18.9 dBic and supports a 40° beam scanning angle in phased-array configurations. Owing to its wide operating bandwidth and switchable CP type, this design offers flexible applicability in Ka-band low earth orbit SATCOMs.

The shrinkage rate of Ni_0.6Zn_0.4Fe_1.8O₄ (NZF) ferrite was controlled to enable cofiring with BaTiO₃ (BTO) at 1250 °C, forming BTO-NZF laminated structures. Postcofiring microstructural analysis revealed a well-bonded interface with minimal elemental interdiffusion. Notably, Ti⁴⁺ exhibited the highest diffusion coefficient (1.60 ± 0.05 × 10^-12 cm²/s). Unidentified phases on the NZF side effectively restricted Ba²⁺ and Ti⁴⁺ diffusion. The BTO-NZF heterojunction consisted primarily of nanoscale amorphous layers containing Ba²⁺ and coherent crystalline regions. The dense amorphous barrier layer not only ensured strong interfacial bonding but also significantly suppressed interdiffusion. High-quality heterojunction formation was influenced by four primary factors, including the presence of similar ionic radii and interplanar spacings, amorphous barrier layers, and a certain concentration of large-radius ions. Magnetic characterization showed that NZF had a saturation magnetization (M_s) of 70.29 ± 0.50 emu/g, a coercivity (H_c) of 8.89 ± 0.50 Oe, and a remanent magnetization (M_r) of 1.01 emu/g. The relative dielectric constant (ε_r) of BTO ranged from 1490 to 2500 (at 1 MHz), while the dielectric loss tangent (tanδ) varied between 4 × 10^-3 and 1.25 × 10^-2. These findings offer valuable guidance for selecting cofired laminated substrates and designing high-performance heterojunctions. Moreover, the resulting cofired laminates exhibit excellent electromagnetic properties, demonstrating strong potential for magnetoelectric coupling applications.

Excellent microwave dielectric properties and ultra-low thermal expansion are essential for dielectric ceramics in high-frequency substrate applications. However, the inherent constrains among these three key microwave dielectric properties make it challenging to simultaneously achieve ultra-low ε_r, high Q×f, and near-zero τ_f values in existing materials. Particularly, the coefficient of thermal expansion of microwave dielectric ceramics often exhibits values around 10 ppm/°C, offering limited tunability. In this work, based on a novel osumilite-type BaMg₂Al₆Si₉O₃₀ ceramic with high crystal structural symmetry and excellent stability, we designed a strategy involving the substitution of Si⁴⁺ with larger Ge⁴⁺ ions. Replacing Si⁴⁺ with larger Ge⁴⁺ ions directly elongated the Si/Al(1)-O bond length while reducing the Si/Al(1)-O(1)-Si/Al(1) angle (σ₂). This structural modification suppressed the longitudinal vibration of 2-coordinate O(1) along the a-axis, effectively inhibiting negative thermal expansion and yielding a reduced CTE within the operational temperature range. Simultaneously, the elongation of the Si/Al(1)-O bond cooperatively increased the Si/Al(1)-O(2)-Si/Al(1) angle (σ₁) and enhanced the relative covalency of the Si/Al(1)-O bond, synergistically improving Q×f values. Importantly, Ge⁴⁺ substitution preserved the ultra-low ε_r and near-zero τ_f values by maintaining the polarization characteristics and crystal structural stability of BaMg₂Al₆Si₉O₃₀-based ceramics. The optimized BaMg₂Al₆Si_7.75Ge_1.25O₃₀ ceramic achieved excellent microwave dielectric properties: ε_r = 5.84, Q×f = 32,351 GHz, τ_f = ‒7.27 ppm/°C, and an ultra-low CTE of +1.07 ppm/°C. The successful co-regulation of the Q×f and CTE values was attributed to the polyhedral coupling strategy, which leveraged the structural features of the osumilite-type ceramics to synergistically optimize the tilting and distortion of critical polyhedra.

In this communication, an ultra-wideband and compact linear-to-circular polarization converter (LTCPC) with good angular stability is presented and analyzed. It is structured as an array by periodic cells, each cell has the same structure and contains two asymmetrical metallic patterns divided by a thin substrate. Specifically, the metallic patterns consist of Jerusalem-cross-like structure (JCLS) on top layer and metal strip on the bottom. The design is optimized by 3D electromagnetic simulation, while the equivalent circuit model analyzes its structure quantitatively. A long crossed branch in JCLS can be equated as a high-pass filter with low cutoff frequency. In addition, this structure can independently change the horizontal and vertical phases to improve the passband. The bottom long strip resonates at a high out-of-band frequency, which can further increase the frequency band of interest. To check its performance, we fabricated and measured a sample with 78×78 cells, each cell’s size is just 0.006λ³₀ (λ₀ is the wavelength corresponding to center frequency). The results reveal that the simulated/measured axial ratios are below 3 dB from 13.7-30 GHz(75%)/14-29.7 GHz(72%) for a normal linear polarized incident wave. Moreover, the scanning angular stability up to 55°, which is useful for wide-angle scanning phased array. Due to the ultra-wide AR bandwidth and high angular stability of the proposed LTCPC, it can simultaneously meet the current application requirements of low earth orbit satellite communications.

Microwave dielectric ceramics are indispensable in modern communication technologies, playing a pivotal role in components such as filters, oscillators, and antennas. Among these materials, ZnAl₂O₄ ceramics have garnered attention for their excellent quality factor (Q × f) and low dielectric constant (ε_r). However, their high sintering temperature (~1650 °C) limits practical applications. This study investigates ZnAl_2-x(Zn_0.5Si_0.5)_xO₄ (ZAZS) (x = 0.1–0.9) ceramics, where [Zn_0.5Si_0.5]³⁺ substitutes Al³⁺, to reduce sintering temperature while maintaining high-performance microwave dielectric properties. ZAZS ceramics were synthesized via the solid-state reaction method and characterized for their structural, morphological, and dielectric properties. X-ray diffraction analysis confirmed the formation of a single-phase solid solution up to x = 0.8, with minor secondary phases appearing at x = 0.9. The substitution increased lattice parameters and enhanced material densification, as observed through SEM and relative density calculations. Microwave dielectric measurements showed that ZAZS ceramics achieved a maximum Q × f of 20,200 GHz and a τ_f value reduced to −62 ppm/°C at x = 0.8, while ε_r decreased from 7.90 to 6.98. Bond-valence calculations reveal that the reduction of the average Al/Zn/Si–O bond valence weakens octahedral rigidity, systematically tuning τ_f toward zero. These results demonstrate that ZAZS ceramics, with a reduced sintering temperature of 1400 °C, exhibit excellent potential for application in low-loss microwave devices.

Recent studies have highlighted the significant influence of external electric fields on the photovoltaic effects of ferroelectric materials. Here, the ferroelectric semiconductor (1-x)Bi_0.5Na_0.4K_0.1TiO₃-xSmCoO₃ (abbreviated as xSmCo, where x ranges from 0.00 to 0.1) was synthesized using the solid-state method, achieving a narrowed optical band gap of 2.20–3.09 eV. Under the combined action of electric and light fields, the short-circuit photocurrent density (J_sc) increases from 44 nA×cm^-2 to 269 nA×cm^-2. When thermal fields are also applied, J_sc further rises to 924 nA×cm^-2. However, the application of additional mechanical or magnetic fields reduces J_sc to 165 nA×cm^-2 and 92 nA×cm^-2, individually. The mixed valence states of Co²⁺/Co³⁺ introduce a high density of oxygen vacancies, facilitating band gap narrowing. The substitution of Sm³⁺ ions at the A-site preserves the ferroelectric properties. In ferroelectric ceramics, remnant polarization (P_r) establishes a strong internal electric field, which is crucial for photo-induced charge carrier dynamics. These findings demonstrate that external fields—light, electric, thermal, mechanical, and magnetic—affect spontaneous polarization strength, internal field stability, and charge carrier transitions within the electronic bands. This study provides new insights into the interplay of multiple field interactions and their effects on the photovoltaic properties (J_sc/V_oc) of ferroelectric oxide materials.

Single-phase BaM₄Si₅O₁₇ (M = Yb, Er, Y, Ho) ceramics have been investigated for their crystal structures, microwave dielectric properties, flexural strength, and potential applications in dielectric antennas. Rietveld refinement and TEM analysis revealed that the BaM₄Si₅O₁₇ ceramics exhibit a monoclinic structure (space groups: P2₁/m). The ε_r of the BaM₄Si₅O₁₇ ceramics was dominated by ionic polarizability and ρ_rel. The Q × f values were considerably larger at BaM₄Si₅O₁₇ (M = Yb and Y) ceramics with the high U_total and low intrinsic dielectric loss. The τ_f values were controlled by the MO₆ octahedron distortion and ^-V_Ba. The flexural strength was mainly dominated by pores and average grain size and reached the maximum value (156 MPa) at BaY₄Si₅O₁₇ ceramic with small average gain sizes and high relative density. Additionally, a patch antenna was fabricated using high-performance BaY₄Si₅O₁₇ ceramic characterized by a ε_r value of 9.02, a Q × f value of 60620 at 12.30 GHz, and a τ_f value of -37.65 ppm/°C. This design achieved a high simulated radiation efficiency of 82.70% and a gain of 5.60 dBi at 6.97 GHz. indicating potential applications of BaY₄Si₅O₁₇ ceramic because of its low dielectric loss and high flexural strength.